The present invention generally relates to a pod for transporting a cassette of semiconductor wafers and more particularly, relates to a semiconductor wafer transport pod equipped with a cover latch indicator to ensure that a cover is latched onto a base before the pod is picked up by an operator.
The high level of automation used in fabricating semiconductor devices relies on sophisticated handling and transport equipment for moving semiconductor wafers between various processing stations. Most handling and transport operations are conducted under automatic control using a programmed computer which issues control signals for operating the equipment with little or no intervention by an operator. In many systems, standard mechanical interface (SMIF) pods are used to transport batches of wafers that are stored in cassettes. These pods include a base upon which the cassettes rest, and a cover removably secured to the base and completely enclosing the cassette. The cover protectively surrounds the cassette, and thus the wafers, from the surrounding environment which may contain airborne, contamination particles. SMIF pods are most often used to transport cassettes from one clean room environment to another, where during the transport movement, the wafers, if not covered, are exposed to the contaminating environment.
After a pod has reached the vicinity of a processing station within a protected, clean room environment, it is necessary to remove the cover so that automated wafer transfer robots can gain access the individual wafers held in the cassette. The covers are held on the pods by various types of latching mechanisms which are automatically actuated to latch and unlatch the cover by means of actuating controls positioned at each processing station. Thus, when a pod reaches a processing station, control mechanisms engage the latch mechanism on the pod to unlatch the cover, following which either an operator or a robotic mechanism removes the cover to expose the cassette. Following processing of a batch of wafers in the cassette, the cover is reinstalled on the pod base, either manually or robotically, after which the control mechanism is actuated to latch the cover on the base before the pod leaves the processing station.
Referring first to FIG. 1, in accordance with the prior art, a pod includes a generally rectangular base 15 upon which there is supported a cassette 12 containing a plurality of vertically spaced, semiconductor wafers (not shown) disposed in stacked relationship to each other. The pod also includes a cover 10 disposed over and protectively enclosing the cassette 12. The cover 10 is provided with a peripheral flange 17 which engages an edge of the base 15, so that the cover 10 is carried on the base 15. A tag 36 is secured to one face of the cover 10 and is used to identify the pod and/or its contents. The tag 36 may comprise a simple bar code device or, an electronic device that can be automatically read by an electronic reader.
The cassette 12 is held on the base 15 by means of an H Bar 18. The H Bar 18 forms a part of the top side of the base, and cooperates to receive a locking member on the base of the cassette 12, in a bayonet like manner.
The base 15 includes a pair of outwardly slidably latch plates 16 having outer fingers 26 which are received in indentations or other recesses (not shown) on the inside wall of the cover 10 in order to lock the cover 10 on the base 15. The latch plates 16 are driven by a circular rotatable plate 24 having a pair of drive pins 28 on the outer periphery thereof. The drive pins 28 are received within elongated slots (not shown) respectively in the latch plates 16. The circular plate 24 is in turn driven by a pair of latch pins 42 that are driven to rotate by other apparatus present at the processing station (not shown) where the pod is delivered in order to load or unload wafers therefrom. Rotation of the plate 24 causes the drive pins 28 to move the latch plate 16 outwardly so that the fingers 26 move into retainers or indentations in the cover 10, thereby latching the latter in place. However, in the event of slight misalignment or tilting of the cover 10 relative to the base 15, or where there is a failure of any of the mechanical driving components, the cover 10 may fail to be properly latched down onto the base assembly 15 but such latching failure is not readily detectable by an operator.
In spite of the fact that positive latch mechanisms are employed to lock the cover on the pod base, occasions arise when, for a variety of reasons, the latch fails to lock the cover on the pod base. This may occur, for example, when a foreign article becomes lodged between the cover and the base or where the cassette becomes tilted on the base, thus interfering with proper seating of the cover. In other cases, the control mechanism for actuating the latch may malfunction. In many cases, failure of the latch mechanism to lock the cover on the pod base goes undetected by process operators. As a result, it is possible that contaminants may pass between the pod base and cover when the pod leaves the clean room environment, thereby resulting in possible contamination of the wafers.
Accordingly, there is a clear need in the art for an improved pod construction which provides a positive indication of when the cover is properly locked down on the pod base. The present invention is directed toward satisfying this need in the art.
It is therefore an object of the present invention to provide a pod for transporting a cassette of semiconductor wafers that does not have the drawbacks or shortcomings of the conventional pods.
It is another object of the present invention to provide a pod for transporting a cassette of semiconductor wafers that is equipped with a cover latch indicator.
It is a further object of the present invention to provide a semiconductor wafer transport pod that is constructed by a base, a cover, a latch means, and an indicator means.
It is another further object of the present invention to provide a semiconductor wafer transport pod equipped with a latch means including four latch keys, a power source and a wiring means in-between the four latch keys.
It is still another object of the present invention to provide a semiconductor wafer transport pod that is equipped with an indicator means of a light emitting diode which is lit when all latch keys are latched onto the cover of the pod.
In accordance with the present invention, a pod for transporting a cassette of semiconductor wafers that is equipped with a cover latch indicator is provided.
In a preferred embodiment, a pod for transporting a cassette of semiconductor wafers is provided which includes a base for supporting the cassette thereon; a cover removably carried on the base for protectively covering the cassette; latch means carried on the base for latching the cover on the base, the latch means is actuatable from a latched position in which the cover is latched on the base to a released position allowing removal of the cover from the base; an indicator means coupled with the latch means for providing a visual indication of the condition of the latch means.
In the pod for transporting a cassette of semiconductor wafers, the latch means may further include at least four latch keys situated around the base, each has an electrically conductive path between two ends of the key; a power source sufficient to activate the indicator means; and wiring means in-between the at least four latch keys, the power source and the indicator means, such that only when all four latch keys are in a latched position, electrical current flows through the wiring means to activate the indicator means. The indicator means may be a light emitting diode, or an indicator lamp. The power source may be a DC power source carried on the base, or a 1.5 V DC battery situated on the base. The wiring means connects the at least four latch keys in series. Each of the at least four latch keys may be situated in a latch key socket that has two electrical switch contacts for connecting by the electrical conductive path on the key. The indicator means may be positioned on a top surface of the cover. The latch means may include four latch keys with two situated on each opposite side of the base.
The present invention is further directed to a pod for transporting a cassette containing a plurality of semiconductor wafers that includes a base for supporting the cassette thereon; a cover removably carried on the base for protectively covering the cassette; latch means carried on the base for latching and unlatching the cover on the base; and means for issuing a visual indication when the cover is latched on the base.
In the pod for transporting a cassette that contains a plurality of semiconductor wafers, the latch means may include four latch keys situated spaced-apart on the base. The means for issuing a visual indication includes an electrical power source, an indicator lamp, and electrical switch means coupled with the power source and the indicator lamp, and actuated by the latch means. The indicator lamp may be a light emitting diode, or a light emitting diode that emits green light. The electrical switch means may further include wiring means connecting the four latch keys in series. The electrical switch means remains in an un-switched position if any one of the four latch keys is in an un-latched position. The electrical power source may be a 1.5 V DC battery. The electrical switch means may further include four latch key sockets each equipped with two electrical switch contacts for connecting by the latch key. Each of the four latch keys may be provided with an electrically conductive path between two ends of the key.